This study is a collaboration with Dr. Victoria Finnerty of Emory University in Atlanta, Georgia. The overall objectives of the project are to understand the genetic basis and regulation of the enzyme beta-glucuronidase in Drosophila and to determine its metabolic role. Studies in the first years have established; (1) Drosophila has three or possibly four forms of the enzyme as observed in isoelectric focusing gels, (2) the principal activity is due to a soluble form of the enzyme of molecular weight 290,000 daltons, (3) optimal assay conditions are virtually identical to those in the mouse. Two types of mutations have been discovered in populations. One type reduces activity fivefold and maps to the tip of the right arm of the third chromosome. Whether this represents the structural locus of the soluble form is as yet unclear. A second type produces an observable alteration in electrophoretic mobility of the soluble form of the enzyme. These latter forms are under intensive investigation.